Human cytomegalovirus (HCMV) is a significant public health concern in the United States. Most important are the effects of the virus on developing fetuses and immunocompromised individuals where it causes a variety of pathological conditions ranging in severity from mild to life-threatening. Since HCMV is present in a persistent or latent form in 50-90% of the world's adult population, the identification of virl gene products that contribute to the establishment and maintenance of a latent infection is an intense and important area of investigation. HCMV encodes 4 GPCR homologs including US28, which has been shown to exhibit both constitutive and agonist-dependent G-protein signaling activities in HCMV infected fibroblasts. Although US28 exhibits high level signaling, it is not essential for lytic viral replication and therefore its function in viral pathogenesis remains unclear. Interestingly, US28 mRNAs are expressed in latently infected hematopoietic progenitors and monocytes, prompting questions regarding the potential role of US28 during latent CMV infections. Our exciting preliminary data indicates that US28 promotes a successful latent infection as US28 null viruses spontaneously enter the lytic phase in hematopoietic cells where wild type virus establishes a latent infection. Therefore, we hypothesize that US28 directed signaling in HCMV infected hematopoietic progenitors leads to the establishment and/or maintenance of latency. To explore this hypothesis, we will take advantage of a newly constructed panel of US28 mutant viruses and recently established methodologies to examine US28 signaling in HCMV infected cells. In Aim 1, we will examine the biological parameters by which US28 drives latency using viral recombinants in primary hematopoietic progenitor cells, and in Aim 2 we will examine the molecular signaling properties of US28 and determine which pathways contribute to the establishment and/or maintenance of latency. Finally, experiments like those proposed in this application are essential for our understanding of the role of CMV GPCRs in viral pathogenesis and will open novel avenues of research for the development of unique antivirals that specifically target the latent reservoir of virus infection.